Inconsistent Seating Depth
- Thread starter leclairk
- Start date
Ned Ludd
Silver $$ Contributor
There can be a number of reasons to explain this phenomenon, many of which have already been covered above. One thing I would point out is that the bullet length inconsistency that might be part of the problem does not lie in the BTO dimension. It would be caused by inconsistent bullet nose length between where the seating die stem contacts the bullet out on the ogive near the nose, and the point on the ogive close to the bearing surface where you caliper insert seats. For that reason, sorting bullets BTO will likely not solve the issue. You might try sorting bullets by OAL and see if that helps; it will do more to actually sort bullets with length variance in the problem region between the seating die stem and caliper insert contact points.
One other thing to consider might be your approach to seating bullets. Regardless of whether there are other underlying causes for your seating depth inconsistency, I would suggest setting the seating die micrometer so that none of your loaded rounds are ever shorter cartridge base-to-ogive (CBTO) than 2.175". From what you described, that will necessarily mean that some will be longer than 2.175". However, you can always put those rounds back in the press after measuring them for an additional stroke, which in my hands will usually seat the bullet from about .0005" to .0015" deeper. If necessary, you can even dial down the micrometer an additional .001" or .002" as necessary, based on your CBTO measurements, then dial it back to the previous setting for the seating the next round. The key is that none of your loaded rounds will end up shorter than your target CBTO length. Yes, it's a little more work that way, but you'll end up with consistent CBTO values for all your loaded rounds. In the meantime, you can figure out what the underlying cause is so the you can correct it.
One other thing to consider might be your approach to seating bullets. Regardless of whether there are other underlying causes for your seating depth inconsistency, I would suggest setting the seating die micrometer so that none of your loaded rounds are ever shorter cartridge base-to-ogive (CBTO) than 2.175". From what you described, that will necessarily mean that some will be longer than 2.175". However, you can always put those rounds back in the press after measuring them for an additional stroke, which in my hands will usually seat the bullet from about .0005" to .0015" deeper. If necessary, you can even dial down the micrometer an additional .001" or .002" as necessary, based on your CBTO measurements, then dial it back to the previous setting for the seating the next round. The key is that none of your loaded rounds will end up shorter than your target CBTO length. Yes, it's a little more work that way, but you'll end up with consistent CBTO values for all your loaded rounds. In the meantime, you can figure out what the underlying cause is so the you can correct it.
I just checked ten of my .260 Rem practice rounds measuring base to ogive, 1 of the ten was .001 short the rest were dead on according to my Starrett dial indicator.
The cases are well into the teens on reloads and the necks are about as work hardened as they come. They have never been annealed and have never been turned. These were loaded with inexpensive practice bullets, Barnes Match Burners @$135 per 500. The cases were sized with a Redding FL bushing die to give me .003 neck compression. The cases were sized and the bullets seated in a Lee Turret press not some finely machined work of art and the kicker is that the seating die is a old Forster Micrometer that I bought when I started shooting .308. I have never bothered buying a .260 seating die. By all reasoning my seating depths should be erratic, yet they are not.
Like I said I am neither bragging or complaining just confused as to why I break all the rules and have no issues
The cases are well into the teens on reloads and the necks are about as work hardened as they come. They have never been annealed and have never been turned. These were loaded with inexpensive practice bullets, Barnes Match Burners @$135 per 500. The cases were sized with a Redding FL bushing die to give me .003 neck compression. The cases were sized and the bullets seated in a Lee Turret press not some finely machined work of art and the kicker is that the seating die is a old Forster Micrometer that I bought when I started shooting .308. I have never bothered buying a .260 seating die. By all reasoning my seating depths should be erratic, yet they are not.
Like I said I am neither bragging or complaining just confused as to why I break all the rules and have no issues
when you least expect it....
Inconsistent neck tension is the most.likely cause.
Use a Expander Mandrel to size the inside of the necks all the same.
HB
Use a Expander Mandrel to size the inside of the necks all the same.
HB
Is the powder being compressed?
I definitely don’t have the expertise that many here do, but I always short seat my bullets, measure CBTO then press the rest of the way in, typically .003-.005” deeper than the initial seating. I tend to have variation of around .002-.003” extreme spread on CBTO after first seating. Anything outside that becomes my foulers.
If you subscribe to nodes in seating depth, depending on what your accuracy needs are, don’t worry too much about it - 0.004” difference can be within your tune window.
All that being said, neck tension definitely affects seating depth. My 3x fired brass without annealing tends to make my seating a little... crunchier than fresh brass
If you subscribe to nodes in seating depth, depending on what your accuracy needs are, don’t worry too much about it - 0.004” difference can be within your tune window.
All that being said, neck tension definitely affects seating depth. My 3x fired brass without annealing tends to make my seating a little... crunchier than fresh brass
What seating stem are you using for your chosen bullet? .002 -.003 is a wide variance for initial seating. With a micrometer top and correct stem, you should be closer to .0005 - .001 delta between rounds. IME, when I switched to a VLD version of the stem to seat hybrid bullets, all the variance tightened up in my seating.
Have you sorted bullets by bullet base to ogive? I have no experience with Berger but I would not be surprised if they vary by a thou or few. I find this with other brands, especially Nosler BT and Accubond. Interestingly Swift Scirocco II 180 gr 30 cal have been very consistent demonstrating 1 or 2 thou variance at the most.
My first step in load development is to find a seating depth accuracy node that is 3 to 5 thou wide with a mid-range powder charge. I have found sub-half moa nodes in two different 30 cal rifles with 150 Accubond and 180 Scirocco II.
Try it. You might like it.
I loaded some test 223 Remington test loads Saturday with Berger 85.5 hybrid target bullets. I had 6 charge weights. The 2 highest charge weights were just beginning to crunch the powder, and gave me a slightly longer CBTO measurement and a couple thousands +/- variance. I have experienced variances before due to inconsistent neck tension and also due to compressing powder.
Thanks for all the info guys. As much as people recommend an arbor press I’m not quite ready to dump my current gear and go in a different direction. I will try sorting my bullets first and see if that makes a difference. I’m using a basic Hornady caliper and insert. Is there a gold standard caliper I should consider?
As far as neck tension, what’s the solution? Will a better sizing die help that? Will my new Whidden die do a better job than my old RCBS die and give me better neck tension or is annealing the only solution?
My process for brass prep is as follows for my once fired Hornady brass, de-prime, wet tumble with SS media, lube with Hornady 1 shot, run my Whidden FL sizer and bump .002, trim with a manual trimmer, prime, and seat.
I should also mention I’m not a BR shooter (that may be obvious). My goal is 1/4-1/2 minute groups consistently out to 1000 yards. Most of my time is spent shooting prone off a bipod at 100-300 yards.
As far as neck tension, what’s the solution? Will a better sizing die help that? Will my new Whidden die do a better job than my old RCBS die and give me better neck tension or is annealing the only solution?
My process for brass prep is as follows for my once fired Hornady brass, de-prime, wet tumble with SS media, lube with Hornady 1 shot, run my Whidden FL sizer and bump .002, trim with a manual trimmer, prime, and seat.
I should also mention I’m not a BR shooter (that may be obvious). My goal is 1/4-1/2 minute groups consistently out to 1000 yards. Most of my time is spent shooting prone off a bipod at 100-300 yards.
jackieschmidt
Gold $$ Contributor
Just a thought.
i use Redding Competition Seaters. I set the die so that the shell holder contacts the bottom of the die body before the linage cams over. That way, I am assured of a firm positive stop.
i use Redding Competition Seaters. I set the die so that the shell holder contacts the bottom of the die body before the linage cams over. That way, I am assured of a firm positive stop.
Tolerance is best determined by your accuracy goal / requirement. IME, 1 or 2 thou can ruin group accuracy if your seating depth node is narrow. Ie; exactly 0.0xx, or if it is only 0.002” wide. Such provides little or no allowance for bullet variability. A 0.003”+ wide node provides much more practical forgiveness.
I use a spinning nylon brush to smooth out the rough carbon inside the case necks , not removing it all just smooth it a bit to ensure consistent seating
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